Code snippets of interest

check_signature(){
# $1 name of file
# $2 keyid
if [ "$2" ] ; then
    keyid=$(gpg --keyserver-options auto-key-retrieve $1.sign 2>&1)
    gpgok=$?
    keyid=$(grep -F "Signature made" <<< "$keyid")
    keyid=${keyid##* }
    if [ "$keyid" != "$2" ] ; then
        echo -e "\n${COLOR_ERROR}Key-ID is not the same as specified in package list${COLOR_NORMAL}"
        echo "${COLOR_ERROR}expected keyid: $2 ${COLOR_NORMAL}"
        echo "${COLOR_ERROR}file '$1' is signed by keyid $keyid instead.${COLOR_NORMAL}"
        [ $gpgok -eq 0 ] && echo "${COLOR_WARN}at least *that* signature is ok ;)"
        return 1
    fi
fi
GPG_OUTPUT=$(gpg --keyserver-options auto-key-retrieve $1.sign 2>&1)
}
#You may need to modify this

sign_pkg(){
# $1: filename of file to be signed
gpg -o $1.sign -b $1
keyid=$(gpg $filename.sign 2>&1 | grep "Signature made")
keyid=${keyid##* }
}
#copypaste this near the end of makepkg's building and call the function if you want it to do it automatically, otherwise you might also want to add an option to sign the resulting file